If you have not already done so, download Avogadro for free and watch the tutorials if necessary.
Import a benzene molecule. Do you see a dipole moment? Watch the tutorial! Explain why.
Now replace the Hs in position 1 and 3 with Cl atoms. Now replace the H in position 5 too. How does the dipole moment change?
Analyse what you have seen by studying the properties of each element in the molecule (sequence Wiew → Properties)